Gas turbines are utilized in a wide variety of applications, such as in power plants for power generation. During the operation of a gas turbine, the efficiency and specific output power at least partly depends on the elevated combustor-firing temperatures of the gas turbine. Associated with a given combustor-firing temperature is an optimal compressor pressure ratio which maximizes the efficiency of the turbine, and increases with increasing combustor-firing temperature. Accordingly, in gas turbines used for power generation, it is typically desirable to operate a compressor at a relatively high pressure ratio to achieve a higher efficiency.
However, operation of a gas turbine at high compressor pressure ratios may lead to stall/surge of the compressor, a condition which arises when the pressure ratio of the compressor exceeds a critical value at a given compressor speed, resulting in a rapid reduction in compressor discharge pressure. The pressure reduction typically results from flow separation from the compressor blades, giving rise to a reversal of flow in the compressor, known as surge. In stall/surge, the compressor performance falls due to the inability of the compressor to handle the excessive pressure ratio, resulting in a rapid drop in the compressor discharge pressure. Stall/surge may further give rise to continual pressure oscillations in the compressor until some corrective action is taken. Thus, the occurrence of stall/surge in the compressor of a gas turbine engine may impair turbine performance and/or lead to the damage within the gas turbine.
To achieve relatively higher efficiency, gas turbines are often operated near surge conditions. Typically, gas turbines are operated at compressor pressure ratios, which are at a sufficient margin away from the surge boundary to avoid unstable compressor operation. In conventional turbine systems, surge protection logic has typically been static. Thus, the surge margin protection logic, once established for a compressor, may be considered fixed and not varied during the compressor operation. Because a static surge protection has to avoid surge even for the worst case compressor operating conditions, the compressor is often overprotected for a significant portion of its operation, resulting in a loss of performance. Moreover, in cases when a plurality of compressor units are in operation, overcompensation may result in some of the compressor units performing well below par affecting the overall efficiency of the system.
Thus, there is a need for improved systems and methods to provide surge protection to one or more compressor units of a gas turbine, while optimizing the performance of each individual unit.